1. Field of the Invention
This invention relates generally to ducting as used in air conditioning systems, and more particularly to a self-tapping fitting capable of connecting together such ducting.
2. Description of the Prior Art
It is customary in the heating, cooling and ventilation field to employ a main, or trunk duct, having extending from it one or more branch ducts. Various fittings have been proposed for connecting a branch duct to an associated main duct. One mannner of attaching a fitting to a duct is shown in U.S. Pat. No. 3,290,066, issued Dec. 6, 1966, to T. Primich, et al, wherein a plurality of tabs are bent over in order to secure a fitting on an associated duct. A significant problem, however, is in cutting a hole in the main duct - which may be constructed from a rigid or flexible metal, reinforced fiberglass, rubber, and the like - prior to insertion and attachment of the branch fitting.
U.S. Pat. Nos. 3,349,792 issued Oct. 31, 1967, to M. E. Larkin, and 3,609,056, issued Sept. 28, 1971, to E. D. Hougen, disclose examples of hole cutters which can be used for tapping holes in air conditioning ducting. A basic disadvantage with this approach, however, is that a large number of cutters must be kept available in order to cut a hole sized to a specific fitting. Further, there can be difficulty in inserting a fitting into a hole cut for it, since it is desirable to have a close fit between the fitting and the hole.
Another problem encountered with the installation of branch duct fittings to main ducts of air conditioning systems, and the like, is that there must be found a manner of attaching the fitting to the duct. Other than the use of the aforementioned bent tabs, it is conventional to employ bolts and similar fasteners which result in projection of an end of a bolt, and the like, into the main duct. Such projections generally are undersirable, in as much as they cause turbulence in the fluid stream within the duct.
Accordingly, it has been proposed to provide quick connection arrangements on duct fittings in order to eliminate the attachment problems referred to above, as well as to assure a good fit between the fitting and an associated duct. Examples of such quick connections can be found in U.S. Pat. Nos. 3,477,745, issued Nov. 11, 1969, to J. W. Williams, et al, and 3,915,477, issued Oct. 28, 1975, to D. R. Timmons. These fittings, intended specifically for use with reinforced fiberglass ducts, employ split rings which permit the connector portion of the fitting to be threaded through a hole previously cut in the associated duct. Once threaded through the duct, the split ring or flange retains the fitting in place on the duct.
With the above approach, however, not only is it first necessary to cut a hole in the associated duct, but insertion of the connector into the hole tends to tear the wall adjacent the hole. This also is the case with U.S. Pat. No. 3,726,545, issued Apr. 10, 1973, to J. R. Grim, et al, which discloses an air duct connector especially for use with reinforced fiberglass ducts and in which the leading edge of the connector is provided with cutting teeth for initially forming a circular aperture in the duct wall. Radially extending tabs are provided for being threaded into the hole, or aperture, so cut so as to lock the connector to the duct wall. Besides tearing a disadvantage of this construction is that the cutting teeth extend into the fluid flow path of the main duct so as to cause turbulence therein. Further, in order to remove the cutout portion of the duct wall from the interior of the duct, which portion will also cause turbulence, air flow restriction, noise, and the like, if retained in the duct, must be done carefully through the mounted fitting in order to avoid the projecting cutting teeth, and the like.
U.S. Pat. No. 3,354,808, issued Nov. 28, 1966, to L. Macrow, discloses an air distribution device provided with a damper arrangable blocking one of two fluid discharge grilles.
Poorly fashioned cuts, such as the pre-cutting of holes by free hand use of a knife, razor blade, and the like, as required in using some of the hereinbefore described prior art fittings, and/or sidewall tearing resulting from use of other above discussed prior art fittings, results in shredding of the fiberglass sidewall materials adjacent the cut holes. In addition to such shredded materials becoming a leakage prone weak spot, shredded fibers must be kept out of the air moving in the duct system to prevent the known health hazzard associated with airborne fibers.